The present invention relates to computer printers and printing materials for use therein, and more particularly, to a computer printing material that will adhere electrostatically to non-conducting surfaces while providing sufficient ink absorbency to allow printing in inkjet printers and the like.
Modern desktop publishing has made possible the production of one of a kind posters and other displays. A user of a conventional personal computer equipped with any one of a number of inexpensive printers can create professional quality artwork and displays. If the user also has access to a scanner, the user can input almost any type of artwork and modify the artwork for inclusion in the user""s own creation. In addition to consumer art works, this type of printing is finding application in point of sale advertising in which the advertising material is printed at the store in which it is to be displayed.
While the ability to generate custom artwork has advanced rapidly, the ability to xe2x80x9changxe2x80x9d the art work has not progressed so rapidly. The options for displaying the artwork can be more or less summarized as xe2x80x9cglue xe2x80x9d, xe2x80x9cframe xe2x80x9d, or xe2x80x9cproject xe2x80x9d. Framing is not cost effective for many temporary displays. In addition, the frame must be mounted on the surface by a fastener or the like. Such fasteners can damage the surface.
Transparency materials for use with overhead projectors have been available for some time. Unfortunately, one needs a projector for each display. While such systems are practical for presentations to groups in business or educational settings, these systems are far from adequate in terms of serving the needs of an artist or teacher who wishes to hang a picture on a wall.
Printer compatible papers with glue backing are also known to those skilled in the publishing arts. These vary in size from small printer labels to full sized sheets. An artwork printed on an adhesive backed sheet may be stuck to a surface without the need to frame the art work or damage the surface by the application of fasteners. Unfortunately, such adhesive backed sheets have a number of problems. First, the artwork cannot, in general, be removed from one location and reapplied at another location more than a few times without the adhesive failing. In addition, some of the adhesives used in these sheets leave a residue on the surface. Furthermore, the adhesives used with some of these papers such as those used for labels are sufficiently strong that the paper may not be removed from surfaces such as glass without destroying the artwork. In some cases, the artwork must be scrapped from the surface using a razor blade or the like.
One type of material that holds the promise of providing a display that sticks to a surface without the use of fasteners or adhesives are the electrets. For the purposes of the present discussion, an electret will be defined to be a plastic sheet which carries an electrostatic charge that persists for an extended period of time. Such sheets can be generated by passing the plastic sheet through an electric field. The resulting plastic sheet will stick to most clean insulating surfaces. Furthermore, the sheet may be easily removed and reapplied to another surface.
Electret compositions for making posters have been described in the prior art. Pads of sheets are commercially sold for use during presentations as a replacement for conventional xe2x80x9cwhite boards xe2x80x9d. These sheets are typically made from polypropylene, which is a few thousandths of an inch thick.
The sheets may be printed via conventional offset printing techniques. In addition, the sheets can be printed in desktop printers that employ dye sublimation or wax transfer. Unfortunately, the sheets are not suitable for printing in inkjet printers that utilize water-based inks. The ink absorbency of the sheets is too small to allow the range of color intensities needed to provide satisfactory artwork. In addition, the sheets require treatment or coatings to render the sheets sufficiently absorbent to accept the water-based inks. In principle, these problems can be overcome by providing a suitable coating on the surface of the sheets; however such sheets tend to curl as the coating expands and contracts with changes in atmospheric humidity.
One method for providing increased ink absorbency is described in U.S. Pat. No. 5,989,685, which is hereby incorporated by reference. In this invention, the ink absorbency is increased by providing an electret material that has xe2x80x9cpits xe2x80x9d in the surface that is to receive the ink. In addition, the surface of the sheet, including the pits, is covered with a hydrophilic coating. While this material has increased ink absorbency, it does not function well in overload situations in which the amount of ink that is deposited at any location is significantly greater that the volume of the pit at that location. The excess ink tends to overflow from the pit and spread over the surface of the printing sheet.
Broadly, it is the object of the present invention to provide an improved printing material that incorporates the advantages of electrets.
It is another object of the present invention to provide a printing material that may be printed in inkjet printers without expensive coating materials.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a printing composition constructed from a printing layer and a blotting layer. The printing layer has a plurality of pores connecting the top and bottom surfaces thereof and is adapted for accepting ink that is retained in the pores. The blotting layer has a top surface that is in contact with the bottom surface of the printing layer. The blotting layer is constructed from a material that has an affinity for the ink that is less than that required to remove the ink from the pores if the pores are not filled with the ink. The printing layer may be constructed from a plastic that has been coated with a surfactant which renders the sides of the pores hydrophilic. The blotting layer may be constructed from a sheet of plastic having pores therein. The blotting layer may also be constructed from a sheet of paper. In the preferred embodiment of the present invention, the printing layer is an electret.